HC-SCR DeNOx Catalysts

1 HC-SCR DeNOx Catalysts. - Since Held and Konig, Held et and 

Iwamoto independently reported the selective catalytic reduction of NOx by 

The efficiency of the above catalysts for NO reduction depends definitely on the kind of metals and their loadings onto supports, the type of reductants and the feed gas composition employed as well as on the kinds of supports and structure of the parent zeolite and its historical nature during preparation. In particular, the effect of the presence of H2O and SO2 in the exhaust gas from mobile sources is well documented on the maintenance of time-on-stream deNOx activity of SCR catalysts, and their resistance to these co-existing gases is an essential parameter determining successful applications to engine sources. The durability of the documented catalysts under hydrothermal conditions should also be considered to verify if those were applicable to controlling vehicle NOx 

Metallosilicates Cu-, Fe-, Ga-, A1-, Co-, Ni-, Mn-, Mo-, Ti-silicate Silicoaluminophosphates Cu-, H-, Ca- and Pd-SAPO, H-MAPO, ALPO Cordierites Mullites 

Single metal oxides AI2O3, Sn02, TiOa, Zr02, La203, Fe304 and Ag20 

---

Hydrothermal Durability of HC-SCR DeNO Catalysts. - Among numerous HC-SCR deNOx catalysts examined, some of the catalysts exhibiting reasonable water tolerance are of particular interest for their commercial use their practical engine applications subsequently require essentially strong hydrothermal stability of the catalyst, particularly zeolite type catalyst. None of the potential SCR catalysts containing appropriate hydrothermal stability for removing NOx from mobile sources have been reported yet. This section will concentrate mainly on the time on-stream stability of potential catalysts for HC-SCR reaction. 

Beneficial Modification of HC-SCR DeNO Catalysts to Improve Hydro-thermal Stability. - Impairment of the hydrothermal durability of HC-SCR catalysts, particularly metal-exchanged zeolites which are of interest in high-temperature deNOx applications, can be either prevented or at least reduced by selecting appropriate parent zeolite structure, employing suitable preparation technique, modifying physicochemical properties, and adding subsequent cation. The former two approaches have been extensively described in the previous section and the other ones will be mainly discussed. 

Most of the exhaust gas stream containing NOx from automotive engines includes H2O in the concentration range of 2 to 18% therefore, the strong water tolerance of deNOx catalysts is essential for its commercial application, in addition to their sulfur tolerance in the presence of SOx also contained in the exhaust stream besides NOx. There have been efforts not only to elucidate the effect of H2O on the deNOx efficiency of HC-SCR catalysts, but also to understand the reason why most of the catalysts significantly lose their activity during the deNOx catalysis in wet A few of... 

---